It is well known that, in general, organic base materials such as organic dyes are affected by the action of light and tend to fade or change in color when exposed to light. Research has been carried out in connection with ink and textile dyes and in the field of photography in order to prevent the occurrence of this type of fading or change in coloration of the organic dyes. In other words, the purpose of this research is to improve the light resistance of these materials. Accordingly, the invention of this application can be usefully employed for improving the light resistance of the organic base materials described above.
In the specification of this application the terms "organic base material" and "base compound" encompass materials which appear to be colored or colorless to the human eye when viewed in sunlight and not just to those substances which have an absorption maximum in the visible range. Optical whiteners or materials which have an absorption maximum in the infrared region are also within the scope of the invention. In the invention of this application the organic base materials include organic substances which have an absorption maximum within the range from about 300 nm in the ultraviolet region to about 2,000 nm in the infrared region.
In the specification of this application the term "dye" encompasses those organic compounds which appear to be colored to the human eye when viewed in sunlight.
Furthermore, in the specification of this application the term "light" signifies electromagnetic radiation of wavelength less than about 2,000 nm and includes ultraviolet radiation of wavelength below about 400 nm, visible light of wavelength from about 400 nm to about 700 nm and near infrared radiation of wavelength from about 700 nm to about 2,000 nm.
It was known in the past that organic base materials, for example, dyes, tended to fade or change color on exposure to light. A number of methods for reducing the extent of any such fading or changes in color, which is to say methods of improving the light resistance of these materials have been reported. For example, in U.S. Pat. No. 3,432,300 it is disclosed that fastness to visible light and ultraviolet radiation can be improved by mixing organic compounds such as indophenol, indoaniline and azo and azomethine dyes with phenol type compounds which have a fused heterocyclic ring system.
In general, azomethine dyes or indoaniline dyes are formed by a reaction between the oxidized form of a primary aromatic amine based developing agent and a color forming agent (a coupler) in the manner described in chapter 17 of The Theory of the Photographic Process, by C. E. K. Mees and T. H. James (published by the Macmillan Co., 1967) for the case of silver halide photographic photosensitive materials. There are also a number of known methods by which the stability of the images formed by these dyes can be improved, which is to say by which the colored images can be stabilized to light. For example, the use of hydroquinone derivatives disclosed in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and British Patent 1,363,921, the use of gallic acid derivatives disclosed in U.S. Pat. Nos. 3,457,079 and 3,069,262 and Japanese Patent Publication No. 13496/68, the use of p-alkoxyphenols disclosed in U.S. Pat. Nos. 2,735,765 and 3,698,909 and the use of chromans and coumarans, etc., such as those disclosed in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990, etc., is well known.
The effect of these above-mentioned prior art compounds is inadequate as agents for the prevention of fading and changes in color.
Furthermore, a method in which the stability to light of organic base compounds is improved by using azomethine quenching compounds such that the absorption maximum is a deeper color than the absorption maximum of the base compounds has been disclosed in British Patent 1,451,000. However, these azomethine quenching compounds are themselves strongly colored so that there is a disadvantage in that they have a considerable effect on the hue of the base material.
It is well known that polymeric compounds such as polyolefins, etc., are degraded by the action of light. Conventional ultraviolet absorbers such as benzophenone derivatives, etc., and hindered amines have often been used to prevent the occurrence of degradation of this type. However, although these compounds have an inhibiting effect on photodegradation of the polymer, they are not really satisfactory.
On the other hand, methods in which metal complexes are used for the stabilization of dyes have been disclosed in British Patent 869,986, U.S. Pat. No. 4,050,938 and Research Disclosure, 15162 (1976), and the use of metal complexes for preventing the photodegradation of polymers is described by O. Chicchetti in Adv. Polymer Sci., 7, 70 (1970), by M. S. Allen and J. F. Mckellar in Chem. Sco. Rev., 4, 533 (1975), by D. J. Carlson and D. M. Wiles in M. Macromol. Sci. Rev. Macromol. Chem., C14, 65 (1976), by R. B. Walter and J. F. Johnson in J. Polymer Sci., 15, 29 (1980) and by N. S. Allen in Chem. Soc. Rev., 15, 373 (1986), etc. However, these complexes do not themselves have a pronounced anti-fading effect or anti-photodegradative effect, nor do they have a high solubility in organic solvents. Furthermore, these complexes are difficult to disperse uniformly within a polymer and it is impossible to add them in amounts which would provide an adequate anti-fading effect or anti-photodegradative effect. Moreover, these complexes are themselves strongly colored so that if they are added in large quantities, they have the disadvantage of having adverse affects on the organic base materials, and especially on the hue and purity of a dye.